A pneumatic device, such as a pneumatic cylinder, is supplied with air from a pneumatic source via a pneumatic line such as piping or hose. By connecting the pneumatic source and the pneumatic device via the pneumatic line, a pneumatic circuit is formed. Air to be supplied from the pneumatic source to the pneumatic device is handled as air to be treated, and the pneumatic circuit is provided with a filter for removing foreign matters, such as water droplets or oil droplets or dusts, contained in the air to be treated.
As one type of the filter provided in the pneumatic circuit, Patent Document 1 discloses a filter having a main block, that is, a port block formed with a primary port and a secondary port, and a filter element attached to the port block. The filter element is adapted to remove foreign matters being composed of liquid droplets such as water droplets or dusts such as powdery and granular materials which are contained in the air to be treated and flowing from the primary port, and to discharge the purified air to the secondary port. In order to receive the foreign matters such as liquid droplets removed by the filter element, a filter bowl, namely, a collection container is attached to the port block.
As a filter to be used in the pneumatic circuit, forms being called air filter, mist filter, and micro mist filter are known, and these filters are defined according to foreign matter removal performance set on the basis of an inner diameter of air holes of a filter element or the like.
A filter adapted to swirl liquid to remove foreign matters mixed in liquid coolant is disclosed in Patent Document 2. This filter is adapted to swirl liquid to remove foreign matters from liquid on the basis of the differences in specific gravity and centrifugal force between the liquid and foreign matters.